Conventional spoon or ladle samplers for collecting samples of molten metal to be solidified and tested for metallurgical composition and properties have now largely been supplanted by small, specially designed sampler molds of glass, ceramic or sheet steel, encased in protective insulating material such as multiple layers of paper or the foamed ceramic insulating material described in my U.S. Pat. No. 3,561,494. These small samplers are carried at the remote end of tubular steel lances which are likewise enclosed in protective insulating material in the manner illustrated in my U.S. Pat. Nos. 3,452,602, 3,686,949 and 4,046,016. These sampler molds are provided with inlet ports closed by a thin protective paper-covered cap of sheet metal cemented in place, and the metal cap closely matches the composition of the melt to be sampled. Upon immersion beneath the surface of the melt, the sheet metal caps are quickly melted and the fluid static pressure of molten metal drives the melt through the immersed inlet port into the interior of the sampler mold, displacing air therefrom through suitable escape vents until the mold is completely filled with molten metal. Being much colder than the melt, the mold withdraws heat from the molten metal inside it, reducing its temperature and causing the sample to solidify inside the mold.
For most metallurgical constituents of normal melt compositions, the operation of these small sampler molds is highly satisfactory. For determination of the constituent percentages of gaseous components having extremely small molecular weights which diffuse rapidly from the solidifying metal, however, these samplers have proved inadequate, since the solidified sample contains only a small proportion of the rapidly diffusing low molecular weight gases such as hydrogen.
Accordingly, complex and expensive sampling and estimating techniques have proved necessary in order to secure even approximate estimates of the percentage of such low molecular weight gases in molten metal compositions.
Maximum hydrogen percentages normally do not exceed two parts per million, making accurate sampling and analysis procedures highly critical.
Currently accepted practice for obtaining molten metal samples for hydrogen analysis involve a large metal spoon which is first coated with slag by dipping it into the melt. Then the spoon is redipped beneath the floating slag layer to a deeper depth within the melt filling the interior of the slag coated spoon with molten metal. The spoon is then withdrawn from the melt and set on the plant floor. An evacuated glass pin sampler mold tube held in a pair of tongs normally manipulated by a second operator is then dipped into the molten metal held in the spoon. The tip of the evacuated glass tube melts off and the vacuum draws the molten metal up inside the tube. Such an evacuated glass tube or tongs cannot be exposed to the normal high melt temperatures inside a furnace because they could not be retrieved before they would melt. Hence the intermediate spoon sampling is a necessity.
During all such procedures, hydrogen is rapidly diffusing from the molten metal held in the spoon, drastically affecting the accuracy of any hydrogen percentage determined by analysis of the sample eventually drawn inside the evaluated glass tube. In addition, the molten metal drawn inside the evacuated glass tube is free to drain out again because there is no chilling means solidifying the molten sample. Because of the vulnerability of the evacuated glass tube sampler, there is no way to take samples directly from a furnace or large ladle and the intermediate sampling spoon procedure cannot be avoided; in addition, there is no way to take samples through a floating slag layer whose high temperature will melt the glass tube before it is immersed through the floating slag.
For all of these reasons, determination of the hydrogen content of molten metal has been extremely difficult or impossible.